Impact resistant propeller system, fast response electric propulsion system and lightweight vertical take-off and landing aircraft using same

ABSTRACT

An aerial vehicle adapted for vertical takeoff and landing using pivoting thrust producing elements for takeoff and landing. An aerial vehicle which is adapted to takeoff with thrust units providing vertical thrust and then transitioning to a horizontal flight path. An aerial vehicle with pivoting thrust units with propellers, wherein some or all of the propellers are able to be stowed and fully nested during forward flight. An aerial vehicle adapted to withstand impacts upon its propellers. An aerial vehicle able to quickly alter the thrust of its propellers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/218,845 to Bevirt et al., filed Mar. 18, 2014, which is hereby incorporated by reference in its entirety.

BACKGROUND

Field of the Invention

This invention relates to powered flight, and more specifically to a vertical take-off and flight control aircraft and flight method.

Description of Related Art

There are generally three types of vertical takeoff and landing (VTOL) configurations: wing type configurations having a fuselage with rotatable wings and engines or fixed wings with vectored thrust engines for vertical and horizontal translational flight; helicopter type configuration having a fuselage with a rotor mounted above which provides lift and thrust; and ducted type configurations having a fuselage with a ducted rotor system which provides translational flight as well as vertical takeoff and landing capabilities.

With VTOL aircraft, significantly more thrust may be required for takeoff and landing operations than during regular forward flight. This extra thrust may also be required during the transitions between vertical and horizontal flight. In the case of propeller driven aircraft, for example, with a plurality of pivoting thrust units using propellers for takeoff, some or many of these thrust units may be idled during regular, horizontal forward flight.

What is called for is a thrust unit utilizing a propeller which allows for rotation of the thrust unit from a position of vertical thrust to a position wherein the thrust unit provides horizontal thrust. What is also called for is a thrust unit which is capable of stowing the propeller blades completely, into a nested configuration.

SUMMARY

An aerial vehicle adapted for vertical takeoff and landing using pivoting thrust producing elements for takeoff and landing. An aerial vehicle which is adapted to takeoff with thrust units providing vertical thrust and then transitioning to a horizontal flight path. An aerial vehicle with pivoting thrust units with propellers, wherein some or all of the propellers are able to be stowed and fully nested during forward flight. An aerial vehicle adapted to withstand impacts upon its propellers. An aerial vehicle able to quickly alter its thrust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an aerial vehicle in a takeoff configuration according to some embodiments of the present invention.

FIG. 2 is a perspective view of an aerial vehicle in a forward flight configuration according to some embodiments of the present invention.

FIG. 3 is a view of a stowing blade system in a deployed forward flight configuration according to some embodiments of the present invention.

FIG. 4 is a perspective view of a stowing blade system in a stowed configuration according to some embodiments of the present invention.

FIG. 5 is a front view of a stowing blade system in a stowed configuration according to some embodiments of the present invention.

FIG. 6 is a partial view of a stowing blade system in a stowed configuration according to some embodiments of the present invention.

FIG. 7 is a front partial view of a stowing blade system in a stowed forward flight configuration according to some embodiments of the present invention.

FIG. 8 is a partial view of a stowing blade system in a stowed configuration according to some embodiments of the present invention.

FIG. 8A is an illustration of a fin mount according to some embodiments of the present invention.

FIG. 9 is a partial view of a stowing blade system in a stowed configuration according to some embodiments of the present invention.

FIG. 10 is a side view of an exemplary blade stowed according to some embodiments of the present invention.

FIG. 11 is a side view of an articulated mounting system in a forward flight configuration according to some embodiments of the present invention.

FIG. 12 is a side view of an articulated mounting system in a take off configuration according to some embodiments of the present invention.

FIG. 13 is a side view of an articulated mounting system in a transitioning configuration according to some embodiments of the present invention.

FIG. 14 is a top view of an articulated mounting system in a transitioning configuration according to some embodiments of the present invention.

FIG. 15 is a perspective view of an articulated mounting system in a transitioning configuration according to some embodiments of the present invention.

FIG. 16 is a partial side view of an articulating mounting system with its blades deployed according to some embodiments of the present invention.

FIG. 17 is a rear perspective view of an articulated mounting system according to some embodiments of the present invention.

FIG. 18 is a partial view of the underside of a rotor hub according to some embodiments of the present invention.

FIG. 19 is a partial side cutaway view of the stowing mechanics according to some embodiments of the present invention.

FIG. 20 is a bottom perspective view of the rotor stowing mechanics according to some embodiments of the present invention.

FIG. 21 is a front view of propeller blade positions according to some embodiments of the present invention.

FIG. 22 is a side view of propeller blade positions according to some embodiments of the present invention.

FIG. 23 is a side partial view of aspects of a blade pivot system according to some embodiments of the present invention.

FIG. 24 is a front view of stowed propeller blades according to some embodiments of the present invention.

FIG. 25 is a side view of stowed propeller blades according to some embodiments of the present invention.

FIG. 26 is a front perspective view of stowed propeller blades according to some embodiments of the present invention.

FIGS. 27A-C are views of a propeller system with different blade coning angles according to some embodiments of the present invention.

FIGS. 28A-F are illustrations of a blade strike according to some embodiments of the present invention.

FIG. 29 is a side view of a rotor deployment mechanism in a stowed configuration according to some embodiments of the present invention.

FIG. 30 is a side view of a rotor deployment mechanism in a deployed configuration according to some embodiments of the present invention.

FIGS. 31A-D illustrate views of an aerial vehicle from take-off to transition to forward flight according to some embodiments of the present invention.

DETAILED DESCRIPTION

Although vertical takeoff and landing (VTOL) aircraft have always been desired, compromises in the realization of these aircraft have limited their usefulness and adoption to certain niches. The thrust needed for VTOL is significantly higher than the thrust needed to maintain horizontal flight. The vertical take-off thrust may also be needed during the transition to forward flight. Once moving in forward flight, the wings of the aircraft provide lift, supplanting a function delivered by motors during VTOL and during transition. Thrust producing elements needed during take-off, but not during forward flight, may be altered during forward flight such that they impart less drag onto the flying system.

In some aspects, an aerial vehicle may use bladed propellers powered by electric motors to provide thrust during take-off. The propeller/motor units may be referred to as rotor assemblies. In some aspects, the motor driven propeller units on the wings may rotate relative to a fixed wing, such that the propellers provide vertical thrust for take-off and landing. The rotation of the motor driven propeller units may allow for directional change of thrust by rotating both the propeller and the electric motor, thus not requiring any gimbaling, or other method, of torque drive around or through a rotating joint. The motor driven propeller units may be referred to herein as motor driven rotor units.

In some aspects, some or all of the wing mounted motor driven rotors are adapted to have the rotor blades fold back into a stowed position wherein the blades nest in recesses in the adjoining nacelle body after a transition to horizontal flight. The nested blades may result in a significantly lower drag of the aerial vehicle, while also allowing a significantly reduced power usage with only some of the rotors providing forward thrust.

In some aspects, extended nacelles with two coaxial propellers are used such that one of the propellers is used during forward flight, and another during vertical take-off and landing. The VTOL propeller may be adapted to nest its blades during forward flight. In some aspects, the extended nacelle may reside at the tip of a wing, or at the end of a rear V-tail element. In some aspects, each of the coaxial propellers has its own electric motor. In some aspects, the coaxial propellers are driven by the same electric motor. In some aspects, the electric motor has directional clutches such that one propeller is driven while the motor rotates in a first direction, and the other propeller is driven while the motor rotates in a second direction.

In some aspects, the mass balance of the aerial vehicle may be altered by movement of masses such as the battery mass. In some aspects, the battery mass may be adjusted to retain balance when a different number of occupants are supported. In some aspects, mass balance may be adjusted in automatic response to sensors within the aerial vehicle. In some aspects, the battery mass may be distributed between a two or more battery packs. The battery packs may be mounted such that their position may be changed during flight in response to changes in the balance of the aerial vehicle. In some aspects, the flight control system of the aerial vehicle may sense differential thrust requirements during vertical take-off and landing, and may move the battery mass in order to achieve a more balanced thrust distribution across the rotor assemblies. In some aspects, the battery mass may be moved should there be a failure of a rotor assembly during transition or vertical take-off and landing, again to balance the thrust demands of the various remaining functioning rotors.

In some embodiments of the present invention, as seen in FIG. 1, an aerial vehicle 100 is seen in take off configuration. The aircraft body 101 supports a left wing 102 and a right wing 103. Motor driven rotor units 140 include propellers 107 which may stow and nest into the nacelle body 106. The aircraft body 101 extends rearward is also attached to raised rear stabilizers 104. The rear stabilizers have rear motors 105 attached thereto. Portions of the rotor unit have been omitted in FIG. 1 for illustrative clarity.

FIG. 1 illustrates the aerial vehicle 100 in a vertical take-off and landing configuration such that the thrust of the rotors is directed upward. The propellers 107 have been rotated relative to the nacelle bodies 106 using articulated linkages. In this vertical take-off and landing configuration, the aerial vehicle 100 is able to utilize six propellers providing thrust in a vertical direction. The propellers 107 are adapted to raise the vehicle 100. After the initial vertical take-off, the vehicle transitions to forward horizontal flight. The transition is facilitated by the articulation of the propellers from a vertical thrust configuration to positions off of vertical, transitioning to a horizontal thrust configuration. FIG. 3 is illustrative of the motor driven rotor unit in a powered forward flight configuration.

As the aerial vehicle 100 transitions to a forward, horizontal, flight configuration, the wings 102, 103 begin to provide lift. Once traveling in a horizontal attitude, with speed, significantly less thrust is needed to propel the aerial vehicle 100 forward than was needed as vertical thrust during take-off. FIG. 2 illustrates a forward flight configuration of an aerial vehicle 100 wherein the blades 108 of the propellers 107 have been stowed into recesses 110 on the nacelle bodies 106. With the blades stowed during forward flight, a low drag profile may be attained. In some aspects, some of the main propellers 107 may be used for forward flight. In some aspects, all of the main propellers 107 may be stowed, and alternate forward flight propellers 111 may be used in forward flight.

In an exemplary configuration of the first embodiment, the aerial vehicle has 6 rotors and weighs 900 kg. The rotor diameters are 2.1 meters, with a thrust per rotor of 1500 N in hover. The continuous rpm of the motor at sea level is 1030 rpm, with a maximum of 1500 rpm. The wingspan is 7.5 meters. The battery mass is 360 kg, and the mass per motor is 9 kg. The cruise speed is 320 km/h. The continuous hover shaft power per motor is 25 kW at standard sea level conditions.

FIGS. 3 and 4 illustrate the deployed and stowed configurations, respectively, of the main propellers 107 of the motor driven rotor units 140. In the deployed configuration, the propeller blades 108 of the propeller 107 are deployed to a position approximately perpendicular to the rotation axis of the motor driven rotor unit 140. The actual blade angle may vary as a function of motor rpm and other factors, as discussed below. A spinner 109 presents a leading surface for the motor driven rotor unit 140.

In the stowed configuration, the blades 108 reside within recesses 110 in the nacelle body 106. As seen in front view in FIG. 5, in the stowed configuration the outer surface of the forward portion of the nacelle is composed of the surfaces of the blades 108 of the propeller 107. The outer surface of the nacelle with the blades in the stowed configuration is a composite of the five blades' surfaces. The blades and the nacelles may be designed in concert such that the nacelle aerodynamic requirements and those of the propeller fit into each other into a complementary design. The recesses 110 may be adapted to provide a very snug fit for the blades 108 in the stowed configuration.

FIGS. 6 and 7 illustrate a perspective view and a front view, respectively, of a motor driven rotor unit with the spinner removed to help the viewer visualize a design according to some aspects of the present invention. The main hub 122 is seen as a mounting point for each of the five propeller blades 108. The main hub 122 provides the main support of the propeller blades, which are each pivotally connected to the main hub. The main hub 122 also provides the drive torque to the blades 108 of the propeller 107. As discussed further below, the main hub 122 is coupled to the outboard bracket of the rotor deployment mechanism via a rotary bearing, or bearing assembly.

FIG. 8 illustrates a perspective view of a motor driven rotor unit with further portions removed for clarity of illustration. The propeller blade 108 is illustrated solely as a partial blade 142, allowing for observation of the fin mount 121. The fin mount 121 is bonded within the (missing in this view) inner portion of the propeller blade. In some aspects, the propeller blade is formed from a number of pre-formed pieces which are then bonded together, with the fin mount affixed therein. The fin mount 121 may be metal, and constructed such that it is adapted to allow for mounting to the main hub 122 with a hinge pin 123, for example. In some embodiments, as seen in FIG. 8A, the fin mount 121 may be a plurality of independent pieces. These pieces may be fixtured during assembly of the propeller blade 108 such that the finished component is adapted to mount to the main hub 122 with a hinge pin. A stowing tab 143 may be affixed to the fin mount 121 to allow for moving the blade into a stowed configuration into the recess and against the nacelle body. In some aspects, the propeller blade 108 may be of a composite material. The propeller blade 108 may be assembled from pieces such that the blade is a hollow shell assembled from pre-manufactured individual pieces. A deploy spring 141 allows for the blades of the propeller to achieve a deployed configuration in the absence of centrifugal forces. The deploy spring allows for full deployment of the propeller blades even when the rotors are not turning. To achieve full stowage, the stowing tabs 143 on the propeller blades 108 of the propeller 107 are pushed on by a stowing mechanism, until the blades are fit within the recesses 110 of the nacelle bodies.

FIG. 9 illustrates another perspective view of a motor driven rotor unit with even further portions removed for clarity of illustration. The main hub 122 is seen supporting the fin mount 121. The fin mount 121 is adapted to pivot relative to the main hub 122 using a hinge pin 123. In some recesses, the partial blades 142 are seen, and other recesses 110 no blade is seen, for purpose of visual clarity only. As the further portions have been removed for illustrative effect, the rotor deployment mechanism, the motor, and other components come into view.

FIG. 10 illustrates a side view of portions of a rotor according to some embodiments of the present invention. The propeller blade 108 is seen in a stowed position. The propeller blade 108 is hinged with a hinge pin 123 to the main hub 122. The main hub is seen mounted within a bearing assembly 125. The bearing assembly 125 is mounted to the outboard bracket 124 of the rotor deployment mechanism. In some aspects, the main hub 122 is mounted to the inner race or races of the bearing assembly 125, and the outer race of the bearing assembly 125 is mounted within the outboard bracket 124 of the rotor deployment mechanism.

FIG. 11 is a side view of portions of a rotor deployment mechanism of a deployable motor driven rotor assembly in a forward flight configuration according to some embodiments of the present invention. The main mounting points 127, 128 are the structural attachment points for the rotor deployment mechanism 143, and by extension, for the motor driven rotor unit, to the aerial vehicle. The drive motor 126 is adapted to drive the rotor main hub 122, and by extension, the propeller of the rotor unit. In this forward flight configuration, the rotor thrust vector is oriented forward with regard to the aerial vehicle, and is horizontal.

FIG. 12 illustrates rotor deployment mechanism 143 in a deployed, vertical take-off, configuration. The rotor deployment mechanism has both rotated and displaced the rotor. The deployment has pushed the rotor hub forward, and away, from the main mounting points 127, 128, as well as upward vertically relative to the main mounting points. In this vertical take-off configuration, the rotor axis is vertical. In some aspects, with the use of rotor deployment mechanisms as described herein, the nacelle may be seen as being split during the rotor deployment such that the rear portion of the nacelle stays with the wing in a fixed positional relationship. The rotor deployment may then be able to occur from a nacelle along the wing, or along a rear horizontal stabilizer element. The rotor deployment mechanisms may be mounted at a position that is not the end of the wing, or other horizontal element.

The outboard bracket 124 is attached to the deployment linkages at the bracket attach points 134, 135. The bracket arms 129, 130, 131 link via pivot points 132, 133. With the use of multi-arm linkages the rotor may be moved to preferred positions in both the deployed and stowed configurations. FIGS. 13-16 illustrate the rotor with its linkages in a partially deployed configuration, which is seen during transitions from vertical to horizontal thrusting, or from horizontal to vertical thrusting.

The electric motor/propeller combination being on the outboard side of the articulating joint allows for a rigid mounting of the propeller to the motor, which is maintained even as the propeller is moved through various attitudes relative to the rear nacelle portion. With such a configuration the rotating power from the motor need not be gimbaled or otherwise transferred across a rotating joint.

FIG. 17 illustrates a deployment drive system for a deployment mechanism according to some embodiments of the present invention. A drive unit 151 may be coupled to the aerial vehicle, within the wing in an area adjacent to the mounting points for the main mounting points 127, 128. Drive screws 150 may be driven such that the deployment linkage is driven from a stowed configuration to a deployed configuration, and from a deployed configuration to a stowed configuration.

FIG. 18 is a partial view of the underside of a main rotor hub 122 mounted into an outboard bracket 124 of a rotor deployment mechanism according to some embodiments of the present invention. A stowing rod 153 is adapted to drive the stowing levers 152 against the stowing tabs 143. The stowing tabs 143 then drive the propeller blades into a nested position onto the nacelle body. The deploy springs 141 are adapted to deploy the propeller blades 108 from a stowed position to a deployed position. FIG. 19 is a partial side cutaway view of the stowing rod 153 coupled to a plurality of stowing levers 152. The stowing rod 153 may be driven by a linear actuator to engage the stowing tabs 143 in order to deploy the propeller blades from their stowed, nested, configuration. When fully deployed, the propeller blades will not reside on the stowing levers. FIG. 20 is a bottom perspective view of the stowing rod 153 and its coupling to the stowing levers 152, and ultimately to the fin mounts 121 of the propeller blades 108. Position indicators may be used to properly line up the propeller relative to the recesses in the nacelle.

In an exemplary embodiment of a method for flying an aerial vehicle with an articulated electric propulsion system and fully stowing blades, an aerial vehicle may be on the ground. The aerial vehicle may have a plurality of wing and tail mounted motor driven rotor units. The motor driven rotor units may begin with propeller blades that are stowed such that the stowed propeller blades comprise all or most of the effective wetted area of portions of the nacelles of which they form a part. The nacelles may have recesses adapted to receive the stowed blades.

The stowed blades may be held in the stowed position with the assistance of stowing mechanisms. In preparation for vertical take-off, the stowed blades may deploy to a deployed configuration. The blades may utilize deployment springs which assist with the deployment of the blades upon the release of stowing levers. The stowing levers may be adapted to pivot the propeller blades from a deployed to a stowed configuration.

Once the propeller blades are in a deployed position, the entire motor driven rotor assembly may be itself deployed from a forward flight position to a vertical take-off and landing position with the use of an articulating rotor deployment mechanism. The deployment mechanism is adapted to position the propellers in front of and above the wings, or otherwise clear of other aerial vehicle structure. With the propeller blades now deployed, and with the motor driven rotor units now articulated into a vertical take-off configuration, the aerial vehicle is able to begin a vertical take-off. The rotors are spun up and the vehicle rises from the ground.

After take-off, the aerial vehicle will begin a transition to forward flight by articulating the rotors from a vertical thrust orientation to a position which includes a horizontal thrust element. As the aerial vehicle begins to move forward with speed, lift will be generated by the wings, thus requiring less vertical thrust form the rotors. As the rotors are articulated further towards the forward flight, horizontal thrust, configuration, the aerial vehicle gains more speed.

Once the aerial vehicle is engaged in regular forward flight, the propellers in use during take-off may no longer be necessary. The thrust requirement for forward flight may be significantly less than that required during vertical take-off and landing. The forward flight may be maintained by just a subset of the propellers used for take-off, or by different propellers than those used during take-off. The unused propellers may have their propeller blades stowed in to recesses on the nacelles supporting the propellers. The stowed propeller blades may form the exterior surface of portions of the nacelle.

In some embodiments of the present invention, as seen in FIGS. 21 and 22, propeller blades 501 may be attached to a central hub 522 such that as the blade pivots from a forward, deployed, position towards a stowed position the blade counter-rotates relative to its normal rotation direction 512. Using the multiple views shown in FIGS. 21 and 22 to illustrate the geometry, the views illustrate the same relative blade positions. In a first position 501 a, 502 a, the blade is coned forward relative to the central hub 522. With this most forward coned position 502 a as seen in FIG. 22, the blade is also rotationally at a most forward position 501 a, as seen in FIG. 21. As the blade moves backwards slightly 502 b relative to the most forward position 501 a, the blade also retards angularly relative to the central hub to a slightly retarded position 501 b.

As the blade moves further backwards, relative to the forward coned position, through more positions 502 c, 502 d, the blade is simultaneously moving back through a series of angularly retarded positions 501 c, 501 d.

Among the advantages of this system is that should a blade be struck by an object, such as a bird, during flight, the system acts in a coupled fashion to lower the impact forces. As the strike hits the blade from the front, the blade is pushed back. The inertia of the impacting object, through its inertia, imparts a force on the blade in an angular direction counter to its undisturbed helical direction of motion. Through the coupling of the system, as the impact causes the blade to pivot backwards relative to a more forward coned position, the coupling retards the blade along its spin direction in such a way that it moves roughly in the direction of the motion of the impacting object, thus moderating the impact upon the blade. Not only is the strain reduced, but the impact shock loading will also be reduced.

The coning angle is achieved as a result of the balance between the aerodynamic and inertial moments generated by the blades. By angling the blade pivot axis relative to a plane normal to the propeller rotational axis, the blade may be made to retard relative to the rotational axis as it is pushed backwards with regard to cone angle. The pivot assembly 523 may have two bores 524, 525. The axis of a first bore 524 closest to the blade 501 may be pushed forward along the spin axis relative to the axis of a second bore 525. This staggering of the bores 524, 525 along a direction parallel to the rotational axis of the propeller and its central hub 522 will allow for the angular retardation of the blade as the blade is pushed backwards from a forward coning angle. When the blade pivot axis is angled as discussed above, the coupled system allows an impacted blade to both slow down and flap backward during the impact, dramatically reducing the impact loads on the blade, the hub, and the support structure.

In some embodiments, in order to help achieve a well nested set of stowed blades which also have good figure of merit, the blades 501 may have some or significant forward sweep. Also, the pivot assembly 523 may be canted in another angle in order to better the nested fit of the set of propeller blades. FIGS. 24, 25, and 26 illustrate front, side, and perspective views, respectively, of a propeller 508 with its blades 501 in a stowed configuration. The outer surfaces of the stowed blades 501 form almost a continuous surface. When stowed over an exterior surface of a nacelle with mating recesses, a very low drag stowed system can be maintained.

FIGS. 28A-F illustrate a series of freeze frames of a rotating propeller 508 being struck by a mass 516. The views illustrate the coupling, as both front and side views are shown from the same moment in time, as the impact affects the system. In these Figures, the propeller is spinning in a clockwise direction 515, with a very forward swept propeller blade. By the later timing in the timed sequence of FIG. 28D, the rotational retardation of the impacted blade can be seen. Also, the downward deflection of the blade can be seen in the side view. By the timed sequence of FIG. 28E, the rotational retardation of the impacted blade can be more clearly seen. Also, the downward deflection of the blade can be more clearly seen in the side view. This sequence illustrates a distinct advantage of this coupled system.

FIGS. 27A-C illustrate top and side views of motor driven rotor assembly according to some embodiments of the present invention. FIG. 27A illustrates a motor driven rotor assembly wherein the propeller is coned backwards somewhat. FIG. 27B illustrates a configuration wherein the propeller blades are substantially perpendicular to the rotational axis. FIG. 27C illustrates a configuration wherein the propeller blades are coned forward.

As mentioned above, the coning angle is achieved as a result of the balance between the aerodynamic and inertial moments on that propeller blade about its hinge axis. FIG. 27C is illustrative of a coning angle which may be seen during normal flight, whether forward flight or vertical take-off and landing. The blades 532 cone up at an angle 530 relative to a plane 531 normal to the spin axis of the propeller. Should there be an increase in the rotational speed of the propeller blade, such as may be desired or required during flight, or during take-off/landing, the resultant increased centrifugal force on the blades, will flatten the blades relative to the initial forward coning angle 530. The resulting position may be as seen if FIG. 27B. The blades 533 are now seen in plane with the normal 531 to the spin axis, although any angle that is closer to normal than the initial forward coning angle 530 may result, depending upon flight parameters and circumstances.

In some embodiments, with the angling of the blade pivot axis as discussed above, the blade pitch will increase as the blade pivots from a more forward coning angle to a flatter coning angle. This change in pitch results as a function of system geometry with the angled pivot pin system.

With the use of electric motors as part of the motor driven rotor assemblies, this system will have an advantage in that very quick responses in thrust are achievable. The electric motors are able to deliver changes in torque very quickly relative to internal combustion engines, or jet engines, for example. An application of increased torque to the propeller hub will result in an initial lag motion of the blades due to their inertia, and this lag motion will result in a change of pitch of the blades. Thus, while the motor is accelerating the pitch of the blades increases. This system, which uses quick to respond electric motors, and also uses a propeller blade system which increases pitch angle with a lag motion of the propeller blades, allows for previously unseen responsiveness in a flight system.

FIG. 29 is a side view of portions of a rotor deployment mechanism of a deployable motor driven rotor assembly in a forward flight configuration according to some embodiments of the present invention. The main mounting points 541, 542 are the structural attachment points for the rotor deployment mechanism 540, and by extension, for the motor driven rotor unit, to the aerial vehicle. The drive motor 543 is adapted to drive the rotor main hub 522, and by extension, the propeller of the rotor unit. In this forward flight configuration, the rotor thrust vector is oriented forward with regard to the aerial vehicle, and is horizontal.

FIG. 30 illustrates rotor deployment mechanism 540 in a deployed, vertical take-off, configuration. The rotor deployment mechanism has both rotated and displaced the rotor. The deployment has pushed the rotor hub 522 forward, and away, from the main mounting points 541, 542, as well as upward vertically relative to the main mounting points. In this vertical take-off configuration, the rotor axis is vertical. In some aspects, with the use of rotor deployment mechanisms as described herein, the nacelle may be seen as being split during the rotor deployment such that the rear portion of the nacelle stays with the wing in a fixed positional relationship. The rotor deployment may then be able to occur from a nacelle along the wing, or along a rear horizontal stabilizer element. The rotor deployment mechanisms may be mounted at a position that is not the end of the wing, or other horizontal element.

The outboard bracket 544 is attached to the deployment linkages at the bracket attach points 134, 135. The bracket arms link via pivot points. With the use of multi-arm linkages the propeller may be moved to preferred positions in both the deployed and stowed configurations.

The electric motor/propeller combination being on the outboard side of the articulating joint allows for a rigid mounting of the propeller to the motor, which is maintained even as the propeller is moved through various attitudes relative to the rear nacelle portion. With such a configuration the rotating power from the motor need not be gimbaled or otherwise transferred across a rotating joint. The deployment is of the entire motor driven rotor in some aspects.

FIGS. 31A-D illustrate an aerial vehicle 600 during take-off and through transition to forward flight according to some embodiments of the present invention. In this illustrative embodiment, the aerial vehicle 600 has a body 601, wings 602, 603, and a tail structure 604. The motor driven rotor assemblies 605 along the midspan of the wing, and attached to the tail structure, have articulating mechanisms adapted to deploy the rotor assemblies. This allows for vertical thrust for take-off and landing, as seen in FIG. 31A. The wing tip rotor assemblies 606 are adapted to pivot to a vertical thrust orientation as well.

After take-off, the rotor assemblies 605, 606 are adapted to transition towards a forward flight configuration, with the thrust moving from a vertical orientation towards a horizontal orientation, via motion of the rotor assemblies, as seen in FIG. 31B. At transition to forward flight, as seen in FIG. 31C, the rotor assemblies 605, 606 have fully transitioned to a horizontal thrust position.

With the lift provided by the wings 602, 603, supporting the aerial vehicle 600, less thrust is needed to keep the vehicle flying horizontally. In order to save power and to reduce drag, the blades 605 of the mid span mounted and rear stabilizer mounted rotor assemblies 605 may have their blades nested against the nacelles. The reduced drag forward flight configuration is illustrated in FIG. 31D.

Nested blades according to some embodiments of the present invention provide a very large decrease in drag. For example, in an illustrative case, feathering blades on an unused motor driven propeller assembly would result in 128N of drag. Simple folding of the blades results in 105N of drag. Yet with nested blades the drag is reduced to 10N. This compares very favorably to a bare nacelle, with 7N of drag.

In some aspects, the blades of the mid span mounted and rear stabilizer mounted rotor assemblies 605 are pivotally attached to a rotor hub. The blades 612 of these rotor assemblies may be forward swept, and attached using an angled pin mechanism as described above. These blades may stow into recesses in the nacelles. The wing tip mounted rotor assemblies 606 may have blades 613 which are variable pitch blades. These blades may power the vehicle during forward flight.

The wing tip mounted blades 613 may rotate in a direction opposite the inner blades along the wing. In addition, the wing tip mounted propeller may rotate such that it counters the tip vortexes of the wings. The wing tip mounted rotor will rotate such that the blades are coming downward 610, 611 exterior to the wings. Thus, the left side wing tip propeller and the right side wing tip propeller will rotate in different directions.

As evident from the above description, a wide variety of embodiments may be configured from the description given herein and additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant's general invention. 

What is claimed is:
 1. An impact resistant propeller system, said impact resistant propeller system comprising: a propeller, said propeller having a primary spin direction along a first spin axis to provide positive thrust, said propeller comprising: a central hub, said central hub comprising a first rotation axis; a plurality of propeller blades, each of said plurality of propeller blades pivotally attached along a first pivot axis to said central hub, wherein the first pivot axis is angled such that pivoting a propeller blade backwards along said first spin axis causes the propeller blade to rotate counter to said primary spin direction.
 2. The impact resistant propeller system of claim 1 wherein said first pivot axis of each of said plurality of propeller blades is angled to a plane normal to the first spin axis.
 3. The impact resistant propeller system of claim 2 wherein said propeller blades comprise a hinge pin, said hinge pin extending from a leading edge of said propeller blade.
 4. The impact resistant propeller system of claim 3 wherein said hinge pin comprises a first end at the leading edge of said propeller blade and a second end away from said leading edge of said propeller blade, and wherein said first end is forward of said second end along said first spin axis.
 5. The impact resistant propeller system of claim 4 wherein said propeller system further comprises a nacelle, and wherein said blades are adapted to pivot from a deployed configuration substantially perpendicular to said spin axis to a stowed position along the exterior of said nacelle.
 6. The impact resistant propeller system of claim 5 wherein said nacelle comprises recesses around its exterior, and wherein said blades reside in said recesses when in said stowed position.
 7. The impact resistant propeller system of claim 6 further comprising a stowing mechanism, said stowing mechanism adapted to stow said propeller blades into said recesses in the outer surface of the nacelle.
 8. The impact resistant system of claim 7 further comprising a spring system adapted to deploy the propeller blades from their stowed position.
 9. The impact resistant propeller system of claim 8 further comprising a propeller deployment mechanism, said propeller deployment mechanism adapted to deploy said central hub from a first position wherein said first spin axis is horizontal to a second position wherein said first spin axis is vertical.
 10. A quick response propeller system for an aerial vehicle, said system comprising: a central hub; a plurality of propeller blades, each of said plurality of propeller blades pivotally attached along a first pivot axis to said central hub, wherein the first pivot axis is angled such that pivoting a propeller blade backwards along said first spin axis from a position forward of normal to the spin axis causes a change in pitch of the propeller blade.
 11. The quick response propeller system of claim 10 further comprising an electric motor coupled to said central hub.
 12. The quick response propeller system of claim 11 wherein said first pivot axis is angled to a plane normal to the first spin axis.
 13. The quick response propeller system of claim 12 wherein said propeller blades comprise a hinge pin, said pivot pin extending from a leading edge of said propeller blade.
 14. The quick response propeller system of claim 3 wherein said hinge pin comprises a first end at the leading edge of said propeller blade and a second end away from said leading edge of said propeller blade, and wherein said first end is forward of said second end along said first spin axis.
 15. The impact resistant propeller system of claim 1 further comprising an electric motor coupled to said central hub.
 16. The impact resistant propeller system of claim 2 further comprising an electric motor coupled to said central hub. 